No, apparently, he isn't.
I do know who vesper 1 is though.
He is Damien Vesper.
The book ' The Medusa plot's end chapter has a preview to who vesper 1 may be.
His description is an old man with a burn on his arm said to be from the cahill family house fire. Damien Vesper was the only vesper there who survived.
But however, the fire happened 500 years from present, we are told.
Probably a formula created by Damien himself. Gideon and Damien were alchemists.
Arthur Trent is a complex character in "The 39 Clues" series who is initially portrayed as an antagonist working for the Lucian branch. However, his true loyalties are revealed to be with the Madrigal branch, making him more of a morally ambiguous character.
Dan and amy's father
Damien Vesper
Vesper Four, the Vesper Scientist is Sandy Bancroft.
Sinead
Vesper Five, the Vesper Spymaster, is Interpol Agent Luna Amato.
Vesper One is the main antagonist in "The 39 Clues" series. Initially, their identity is unknown to the Cahill family members who are searching for the 39 Clues, but Vesper One's goal is to find all 39 Clues for their own mysterious agenda. Throughout the series, Vesper One's true identity and motives are gradually revealed.
suspected vesper hideout
vesper target sunk
Vesper two
vesper two
vesper target sunk